Usage of z64/None as "no transaction" marker is inconsistent

[Christian Theune]

While working on Bug #181712 we discovered that the use of z64 or None as the marker for "no previous transaction" is inconsistent.

In the original bug we decided that we should make it consistent. I'm opening another bug specially for this because this is out of scope for the originally reported bug.

[Jim Fulton (jim-zope)]

Is this still an issue? If so, could you please be more specific? Where and in what way are signaling of "no previous transaction" inconsistent?

[Christian Theune (ctheune)]

In the case of empty storages:

MappingStorage: lastTransaction returns ltid which is initialized with None
FileStorage: lastTransaction returns ltid with is initialized with the index which uses z64 on empty storages
DemoStorage: lastTransaction returns what its base returns
ClientStorage: returns None

So by looking at it, it's basically FileStorage which returns z64, the others tend to use None.

Some details of this were already discussed around here https://bugs.edge.launchpad.net/zodb/+bug/181712/comments/7 but haven't been checked in because the patch never got feedback.

[Jim Fulton (jim-zope)]

will be in 3.10 b7